Electrolysis tank used for aluminum electrolysis and electrolysis process using the electrolyzer

ABSTRACT

An electrolytic cell for aluminum electrolysis includes a cell body, in which an anode and a cathode are arranged inside the cell body, the cell body is filled with an electrolyte, and at least a part of the anode is immersed in the electrolyte; the anode is arranged above the cell body, the cathode is arranged at the bottom of the electrolytic cell and is covered by aluminum liquid, the electrolyte is located between the anode and the cathode and covers the aluminum liquid; and an insulating layer is arranged on the inner sidewall of the cell body for isolating oxygen or the electrolyte from a carbon block. The anode contains Fe and Cu as primary components; and the electrolyte is composed of 30-38 wt % of NaF, 49-60 wt % of AlF 3 , 1-5 wt % of LiF, 1-6 wt % of KF and 3-6 wt % of Al 2 O 3 , and the molar ratio of NaF to AlF 3  is 1.0-1.52.

FIELD OF THE INVENTION

The present invention relates to an electrolytic cell for aluminumelectrolysis and an electrolysis process using the electrolytic cell,belonging to non-ferrous metal smelting industry.

BACKGROUND OF THE INVENTION

In aluminum electrolysis industry, a traditional Hall-Heroult moltensalt aluminum electrolysis process is typically adopted to performelectrolysis on the molten salts of cryolite-alumina in a prebakedcarbon anode electrolytic cell typically by adopting, that is, cryoliteNa₃AlF₆ fluoride salt melt is taken as flux, Al₂O₃ is dissolved in thefluoride salt, a carbon body is taken as an anode and verticallyinserted into the electrolytic cell, a carbon body with aluminum liquidcovering the bottom of the electrolytic cell is taken as a cathode,electrochemical reaction is carried out on the anode and cathode of theelectrolytic cell at a high temperature ranging from 940 to 960° C.after a strong direct current is introduced, and the resultant aluminumliquid product covers the cathode at the bottom of the electrolyticcell. Due to high electrolysis temperature, the traditional aluminumelectrolysis process has such characteristics as large volatilizationamount of electrolyte, large oxidization loss of a carbon anode, largeenergy consumption and poor working environment.

In the prior art, in order to lower electrolysis temperature, a lowtemperature molten salt system for aluminum electrolysis is disclosed inChinese patent document CN101671835A, the molten salt composition of thesystem includes AlF₃, Al₂O₃ and one or more salts selected from thegroup consisting of KF, NaF, MgF₂, CaF₂, NaCl, LiF, and BaF₂, and theelectrolysis temperature of the electrolyte can be lowered to be withina wide area from 680 to 900° C. for the purpose of operations.

Addition of NaCl to the aforementioned electrolyte aims at lowering theliquidus temperature of the electrolyte, however, NaCl will lead tocorrosion to metal parts like electrolytic cell accessories at theaforementioned electrolysis temperature, furthermore, NaCl is extremelyliable to volatilization in the electrolysis process so as to form HCltoxic gas, so its application is difficult; in addition to addition ofNaCl, decrease of the molar ratio of NaF to AlF₃ can also lower theliquidus temperature of the electrolyte in light of common knowledge inthis art, but in the existing industry, the molar ratio of NaF to AlF₃is generally larger than 2.2, this is because, if the molar ratio of NaFto AlF₃ further decreases, NaF and AlF₃ will lead to a ‘crusting’phenomenon of the cathode in the process of low-temperature electrolysiswhile the liquidus temperature of the electrolyte is lowered, the reasonfor this ‘crusting’ phenomenon is that sodium ions and aluminum ions inthe electrolyte will gather at the cathode in the electrolysis processto generate sodium cryolite, which is seldom molten at a low temperaturedue to its high melting point, as a result, the surface of the cathodeis covered by a layer of refractory cryolite crust to affect normalelectrolysis in the electrolysis process tremendously. Due to the aboveproblems in the prior art, industrial application of the electrolyte issignificantly limited, and it is an unsolved problem in the prior art tofind a way of avoiding corrosion to electrolysis devices and damage tohuman body and ensuring proper electric conductivity and aluminasolubility as well as no cathode ‘crusting’ phenomenon of the preparedelectrolyte while the liquidus temperature of the electrolyte is furtherlowered.

In addition to the high electrolysis temperature problem that needs tobe solved, the carbon anode in the traditional electrolytic cell foraluminum electrolysis is ceaselessly consumed by oxidization in theelectrolysis process, thus constant replacement for the carbon anode isrequired; moreover, carbon dioxide, carbon monoxide and other wastegases are continuously generated at the anode during aluminumelectrolysis. Hence, to lessen the consumption of an anode material inthe aluminum electrolysis process and simultaneously reduce the emissionof waste gases, disclosed in the prior art is plenty of documents forresearch on anode material, e.g. disclosed in Chinese patent documentCN1443877A is an inert anode material applied to aluminum, magnesium andrare earth electrolysis industries, this material is formed by binary ormulti-element alloy composed of chromium, nickel, ferrum, cobalt,titanium, copper, aluminum, magnesium and other metals, and thepreparation method thereof is a smelting or powder metallurgy method.The prepared anode material is good in electric and thermal conductivityand generates oxygen in the electrolysis process, wherein in Example 1,an anode is made of the alloy material composed of 37 wt % of cobalt, 18wt % of copper, 19 wt % of nickel, 23 wt % of ferrum and 3 wt % ofsilver and is used for aluminum electrolysis, the anode has a currentdensity of 1.0 A/cm² in the electrolysis process at 850° C. and the cellvoltage is maintained within a range from 4.1V to 4.5V in theelectrolysis process, the prepared aluminum has a purity of 98.35%.

Compared with the carbon material, the alloy anode material in thetechnologies aforementioned has higher electric conductivity and lowercorrosion amount in the electrolysis process and can be processed intorandom shapes, however, the alloy anode composed of the aforementionedcomponents is still high in overvoltage, which results in largeindustrial power consumption and low product quality, besides, since alarge quantity of expensive metal materials are used, the anode materialis high in cost and cannot adapt to industrial needs.

In addition, a layer of oxide film is generated on the surface of theprepared alloy anode in the prior art, and if this oxide film isdestroyed, the anode material exposed to the surface will be oxidized asa new oxide film. The oxide film on the surface of the alloy anode inthe prior art has low oxidization resistance and is further liable tooxidization reaction to generate products that are likely to be corrodedby the electrolyte, and the oxide film with low stability is liable tofall off the anode electrode in the electrolysis process; after theprevious oxide film is corroded or falls off, the material of the alloyanode exposed to the surface will create a new oxide film by reaction,such replacement between new and old oxide films results in continuousconsumption and poor corrosion resistance of the anode material;furthermore, the corroded or falling oxide film enters into liquidaluminum in the electrolysis process of alumina to degrade the purity ofthe final product aluminum, as a result, the manufactured aluminumproduct cannot meet the demand of national standards and accordinglycannot be directly used as a finished product.

SUMMARY OF THE INVENTION

The first technical problem to be solved by the present invention isthat, the prior art is incapable of avoiding corrosion to electrolysisdevices and damage to human body and ensuring proper electricconductivity and alumina solubility as well as no ‘crusting’ phenomenonin the prepared electrolyte while the liquidus temperature of theelectrolyte is further lowered. Thus the present invention provides anelectrolytic cell, containing an electrolyte for aluminum electrolysiswhich is low in liquidus temperature, free from metal corrosion, notliable to volatilization, proper in electric conductivity and aluminasolubility and free from cathode ‘crusting’ phenomenon.

Simultaneously, the second technical problem to be solved by the presentinvention is that, an alloy anode composed of metal components in theprior art is high in overvoltage, power consumption in the aluminumelectrolysis process is large and the metal components employed are highin price, resulting in cost increment of the alloy anode; in addition,an oxide film on the surface of the alloy anode in the prior art is lowin oxidation resistance and liable to fall off, which leads tocontinuous consumption of the alloy anode and poor corrosion resistance,furthermore, the corroded or falling oxide film enters into liquidaluminum to degrade the purity of the final product aluminum; andtherefore, provided is an electrolytic cell for aluminum electrolysis,which is low in overvoltage of the used inert anode material, low inprice, strong in oxidation resistance and stability of the oxide filmformed on the surface thereof and resistant to electrolyte corrosion.

Simultaneously, the present invention provides a process for aluminumelectrolysis using the above electrolytic cell.

To solve the aforementioned technical problems, the present inventionprovides an electrolytic cell for aluminum electrolysis, comprising acell body, wherein an anode and a cathode are arranged inside the cellbody, the cell body is further filled with an electrolyte; the anode isarranged above the cell body, and at least a part of the anode isimmersed in the electrolyte; the cathode is arranged at the bottom ofthe electrolytic cell and covered by a certain amount of aluminumliquid; the electrolyte is located between the anode and the cathode;the anode contains the components including Fe, Cu, Ni and Sn, whereinFe and Cu serve as primary components; the electrolyte is composed of30-38 wt % of NaF, 49-60 wt % of AlF₃, 1-5 wt % of LiF, 1-6 wt % of KFand 3-6 wt % of Al₂O₃, wherein the molar ratio of NaF to AlF₃ is1.0-1.52.

The bottom surface of the anode is kept parallel to the cell body, andan insulating layer is arranged on the inner sidewall of the cell bodyand is used for isolating oxygen or the electrolyte from a carbon block.

A cell cover is arranged at the upper end of the cell body and isprovided with a vent and a feeding hole; a cathode bar is arrangedinside the cathode, one end of the anode penetrates through the cellcover and is connectedly provided with a binding post for connectionwith a power supply.

The mass ratio of Fe to Cu to Sn is (23-40):(36-60):(0.2-5).

The components of the anode further include Ni.

The anode is composed of Fe, Cu, Ni and Sn, wherein the content of Fe is23-40 wt %, the content of Cu is 36-60%, the content of Ni is 14-28 wt %and the content of Sn is 0.2-5 wt %.

The components of the anode further include Al and Y.

The anode is composed of Fe, Cu, Ni, Sn, Al and Y, wherein the contentof Fe is 23-40 wt %, the content of Cu is 36-60 wt %, the content of Niis 14-28 wt %, the content of Al is more than zero and less than orequal to 4 wt %, the content of Y is more than zero and less than orequal to 2 wt %, and the content of Sn is 0.2-5 wt %.

The molar ratio of NaF to AlF₃ is 1.12-1.52.

The liquidus temperature of the electrolyte is 620-670° C.

An electrolysis process using the electrolytic cell comprises the stepsof:

(1) adding specified amounts of NaF, AlF₃, LiF, KF and Al₂O₃ to amelting furnace for mixing and melting to form a melt; or addingspecified amounts of NaF, AlF₃, LiF and KF to a melting furnace formixing and melting, and then adding Al₂O₃ to obtain a melt; and(2) raising the temperature of the melt prepared in step (1) to above720-760° C., and then, pouring the melt into the electrolytic cell andcarrying out electrolysis while the temperature is maintained at720-760° C.

The electrolysis temperature is 730-750° C.

Al₂O₃ is quantitatively supplied in the electrolysis process.

The electrolysis process using the electrolytic cell comprises the stepsof:

(1) adding specified amounts of NaF, AlF₃, LiF, KF and Al₂O₃ to amelting furnace for mixing and melting to form a melt; or addingspecified amounts of NaF, AlF₃, LiF and KF to a melting furnace formixing and melting, and then adding Al₂O₃ to obtain a melt; and(2) raising the temperature of the melt prepared in step (1) to above720-760° C., and then, pouring the melt into the electrolytic cell andcarrying out electrolysis while the temperature is maintained at720-760° C.

The electrolysis temperature is 730-750° C.

Al₂O₃ is quantitatively supplied in the electrolysis process.

The electrolytic cell and the electrolysis process using theelectrolytic cell in the present invention have the advantages below:

(1) The electrolytic cell for aluminum electrolysis in the presentinvention comprises a cell body, wherein an anode and a cathode arearranged inside the cell body, and the cell body is further filled withan electrolyte; the anode is arranged above the cell body, and at leasta part of the anode is immersed in the electrolyte; the cathode isarranged at the bottom of the electrolytic cell and covered by a certainamount of aluminum liquid; the electrolyte is located between the anodeand the cathode; the anode contains the components including Fe, Cu, Niand Sn, wherein Fe and Cu serve as primary components; the electrolyteis composed of 30-38 wt % of NaF, 49-60 wt % of AlF₃, 1-5 wt % of LiF,1-6 wt % of KF and 3-6 wt % of Al₂O₃, wherein the molar ratio of NaF toAlF₃ is 1.0-1.52.

The anode containing metal Sn and composed of the aforementioned metalcomponents is high in electric conductivity and low in overvoltage, thecell voltage in the electrolysis process of the electrolytic cell isabout 3.1-3.4V, power consumption in the aluminum electrolysis processis small, the power consumption for per ton of aluminum is not more than11000 kw·h, so the process cost is low; the anode material is alloycomposed of Fe, Cu and Sn, so an oxide film formed on the surface of theanode in the electrolysis process is high in oxidation resistance and ishardly corroded by the electrolyte, and the formed oxide film is stableand not liable to fall off, therefore, the anode is imparted with quitehigh oxidation resistance and strong corrosion resistance so as toensure the purity of aluminum products, that is, the purity of theproduced aluminum can reach 99.8%. The following problems in the priorart are avoided: the alloy anode has high overvoltage, the oxide film onthe alloy surface is low in oxidation resistance and liable to fall off,which leads to continuous consumption of the alloy anode and poorcorrosion resistance, furthermore, the corroded or falling oxide filmenters into liquid aluminum to degrade the purity of the final productaluminum. In addition, Fe and Cu serve as primary components of thealloy anode and their content proportions are quite high, andaccordingly, the manufacturing cost of the anode material is lowered.

The used electrolyte employs a pure fluoride system, substancecomposition in the electrolyte is defined, the contents of thesesubstances are further defined and the molar ratio of NaF to AlF₃ is1.0-1.52, so that the liquidus temperature of the electrolyte is loweredto 640-670° C., as a result, electrolysis can be carried out at 720-760°C. according to the electrolysis process, which reduces volatilizationloss of fluoride salt, avoids corrosion to electrolysis devices anddamage to human body, improves working environment, greatly reducesenergy consumption in the electrolysis process and achieves the aim ofenergy saving and emission reduction; meanwhile, in the presentinvention, proper amounts of LiF and KF are added and can be combinedwith sodium ions and aluminum ions in the electrolyte to form lithiumcryolite and potassium cryolite with low melting points, thus thecrusting phenomenon is avoided in the electrolysis process; comparedwith the existing industry, the electrolyte for aluminum electrolysis inthe present invention has no CaF₂ and MgF₂ added therein, instead, KF inan appropriate proportion, which has the function of increasing aluminasolubility and dissolution velocity, is added to a system in which themolar ratio of NaF to AlF₃ is 1.0-1.52, therefore, the shortcoming oflow alumina solubility in the low-molar-ratio electrolyte is improved;in general, the electric conductivity of the electrolyte decreases asthe temperature decreases, so typically, the electric conductivity at alow electrolysis temperature hardly meets the demand in a normalelectrolysis process; the electrolysis temperature is lowered bylowering the liquidus temperature of the electrolyte in the presentinvention, however, the electric conductivity of the electrolyte at alow temperature can still meet the demand in the electrolysis processbecause LiF with a larger electric conductivity is added and componentproportions in the electrolyte are optimized, thus enhancing the currentefficiency in the electrolysis process. According to the invention, thecontent of LiF is defined as 1-5%, this is because too low content ofLiF fails to improve electric conductivity and to prevent crusting, andtoo high content of LiF results in decrease of the alumina solubility,and the above two situations are effectively avoided by defining thecontent of LiF as 1-5% in the present invention; and there is nocorrosion to a metal device when the electrolyte with the aboveproportions in the present invention is used, in this way, the servicelife of the electrolysis device is prolonged.

(2) In the electrolytic cell for aluminum electrolysis in the presentinvention, the anode is composed of Fe, Cu, Ni, Sn, Al and Y, whereinthe content of Fe is 23-40 wt %, the content of Cu is 36-60 wt %, thecontent of Ni is 14-28 wt %, the content of Al is less than or equal to4 wt %, the content of Y is less than or equal to 2 wt %, and thecontent of Sn is 0.2-5 wt %.

Similarly, the aforementioned inert alloy anode has the advantages oflow material cost and high electric conductivity, in addition, the metalAl contained in the aforementioned inert alloy anode plays a role ofoxidization resistance and can serve as a reducing agent formetallothermic reduction reaction with metal oxides in the inert anodealloy, thus preventing the metals in the inert alloy anode, i.e. primarycomponents, from being oxidized, and causing reduction of the electricconductivity of the alloy anode; meanwhile, the metal Y added can beused for controlling a crystal structure for anode material formation inthe preparation process of the inert anode, achieving theanti-oxidization purpose.

(3) In the electrolytic cell for aluminum electrolysis in the presentinvention, specified amounts of NaF, AlF₃, LiF, KF and Al₂O₃ are mixed,the resultant mixture is heated to form a melt; or specified amounts ofNaF, AlF₃, LiF and KF are mixed, the resultant mixture is heated untilthe mixture is molten, and then Al₂O₃ is added to obtain a melt;afterwards, the melt prepared is electrolyzed at 720-760° C.Electrolysis temperature is directly associated with volatilization ofthe electrolyte, cathode crusting phenomenon, energy consumption of theprocess, electric conductivity and alumina solubility, and the inventorof the present invention, by long search, set the electrolysistemperature within a range from 720-760° C. in a matching way based onthe components and content characteristics of the electrolyte in thepresent invention, thus the cathode crusting phenomenon is prevented andvolatilization of the electrolyte and energy consumption of theelectrolysis process are remarkably reduced while both the electricconductivity and the alumina solubility are increased, and the economicefficiency of the process is improved. Preferably, the electrolysistemperature is further set within a range from 730-750° C. in thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For more easily understanding the contents of the present invention,further description will be made below to the technical solution of thepresent invention in conjunction with the drawing and the embodiments.

FIG. 1 is a structure diagram of the electrolytic cell for aluminumelectrolysis in the present invention;

In this drawing, reference signs are as follows: 1 refers to cell body,2 refers to anode, 3 refers to cathode, 4 refers to electrolyte, 5refers to insulating layer, 6 refers to cell cover, 7 refers to vent, 8refers to feeding hole, 9 refers to binding post, 10 refers to cathodebar and 11 refers to aluminum liquid.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The electrolytic cell for aluminum electrolysis in the present inventionis as shown in FIG. 1 and comprises a cell body 1, wherein an anode 2and a cathode 3 are arranged inside the cell body 1, the anode 2 and thecathode 3 can be arranged in random ways in accordance with the actualneed, in this embodiment, the anode 2 is arranged above the cell body 1,the bottom surface of the anode 2 is kept parallel to the cell body 1,the cathode 3 is arranged at the bottom of the electrolytic cell andcovered by a certain amount of aluminum liquid 11; the cell body 1 isfurther filled with an electrolyte 4, immersion of the anode 2 and thecathode 3 in the electrolyte 4 depends on the selected electrolytic cellstructure, in this embodiment, at least a part of the anode 2 isimmersed in the electrolyte 4; the cathode 3 is arranged at the bottomof the electrolytic cell and covered by a certain amount of aluminumliquid 11; the electrolyte 4 is located between the anode 2 and thecathode 3 and covers the aluminum liquid 11; the anode 2 contains thecomponents including Fe, Cu, Ni and Sn, wherein Fe and Cu serve asprimary components, and the molar ratio of Fe to Cu to Sn is(23-40):(36-60):(0.2-5); the electrolyte 4 is composed of 30-38 wt % ofNaF, 49-60 wt % of AlF₃, 1-5 wt % of LiF, 1-6 wt % of KF and 3-6 wt % ofAl₂O₃, wherein the molar ratio of NaF to AlF₃ is 1.0-1.52, preferably1.12-1.52, and the liquidus temperature of the electrolyte 4 is 620-670°C., preferably 640-670° C.

As a variable embodiment on this basis, in order to isolate the innersidewall of the cell body 1 from the electrolyte 4 and oxygen to preventtransfer of electrons between the sidewall of the cell body 1 and theelectrolyte 4 and corrosion of the electrolyte 4 to the sidewall of thecell body 1, an insulating layer 5 is arranged on the inner sidewall ofthe cell body 1 and is made of any commercially available insulatingmaterial that is resistant to high temperature and corrosion of theelectrolyte 4, e.g. corundum, aluminate spinel refractory and the like.In this embodiment, a carbon block is arranged between the innersidewall of the cell body 1 and the insulating layer 5, and the carbonblock and the cathode 3 are integrally formed. Undoubtedly, the carbonblock and the cathode 3 can also be arranged in a separated manner.

On this basis, in order to isolate the electrolysis environment for theelectrolytic cell from outside without impediment to exhaust andfeeding, a cell cover 6 is arranged at the upper end of the cell body 1and is provided with a vent 7 and a feeding hole 8 thereon, the sizesand positions of the vent 7 and the feeding hole can be randomlydetermined in accordance with the actual need, and in this embodiment,the vent 7 is arranged next to the anode 2.

Further, in order to facilitate connection of the anode 2 and thecathode 3 with a power supply, a cathode bar 10 is arranged on thecathode 3 at the bottom of the electrolytic cell and is used forconnection with the power supply of the cathode 3; one end of the anode2 penetrates through the cell cover 6 and is connected and provided witha binding post 9 for connection with the power supply of the anode 2;and the cathode 10 and the binding post 9 can be made of any materialwith good electric conductivity, including steel, iron and alloymaterials, etc.

On this basis, in order to improve the combination firmness among metalsFe, Cu and Sn, the components of the anode 2 further include Ni,preferably the anode 2 is composed of Fe, Cu, Ni and Sn, wherein thecontent Fe is 23-40 wt %, the content of Cu is 36-60 wt %, the contentof Ni is 14-28 wt % and the content of Sn is 0.2-5 wt %.

The anode 2 may be preferably composed of Fe, Cu, Ni, Sn, Al and Y, theadded Al can prevent other primary metal components of the anode 2 fromoxidation and improve the oxidization resistance, the component Y can beused for regulating and controlling the structure of the prepared alloycrystal in order to achieve the anti-oxidization purpose, wherein thecontent of Fe is 23-40 wt %, the content of Cu is 36-60 wt %, thecontent of Ni is 14-28 wt %, the content of Al is less than or equal to4 wt %, the content of Y is less than or equal to 2 wt %, and thecontent of Sn is 0.2-5 wt %.

The electrolysis temperature is 720-760° C. when the aforementionedelectrolytic cell is used for aluminum electrolysis, preferably 730-750°C.

Description is made below in conjunction with the embodiments.

Embodiment 1

Fe, Cu, Ni and Sn metal blocks are mixed based on 23 wt % of Fe, 60 wt %of Cu, 14 wt % of Ni and 3 wt % of Sn, the mixture is molten by heatingat high temperature and then subjected to casting to obtain an anode 1.The anode 1 has a density of 8.3/cm³, a specific resistivity of 68 μΩ·cmand a melting point of 1360° C.

The components of the electrolyte in this embodiment are as follows: 32%of NaF, 57% of AlF₃, 3% of LiF, 4% of KF and 4% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.12. The liquidustemperature of the electrolyte in this embodiment is 640° C. accordingto measurement. The electrolyte has an electric conductivity of about1.7 Ω¹·cm⁻¹, a density of about 2.03 g/cm³ and an alumina saturationconcentration of 5%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 1 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF, KF and Al₂O₃ in a meltingfurnace so as to form a melt; and(2) raising the temperature of the melt prepared in step (1) to above720° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 720° C., wherein Al₂O₃ is quantitativelysupplied in the electrolysis process.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.1 V, the powerconsumption for per ton of aluminum is 10040 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.85%.

Embodiment 2

Fe, Cu, Ni and Sn metal blocks are mixed based on 40 wt % of Fe, 36 wt %of Cu, 19 wt % of Ni and 5 wt % of Sn, the mixture is molten by heatingat high temperature and then subjected to casting to obtain an anode 2.The anode has a density of 8.1/cm³, a specific resistivity of 76.8 μΩ·cmand a melting point of 1386° C.

The components of the electrolyte in this embodiment are as follows: 38%of NaF, 50% of AlF₃, 2% of LiF, 5% of KF and 5% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.52.

The performances of the electrolyte in this embodiment are measured andthe measurement result is that the liquidus temperature of theelectrolyte in this embodiment is 670° C. The electrolyte has anelectric conductivity of about 1.8 Ω⁻¹·cm⁻¹, a density of about 2.05g/cm³ and an alumina saturation concentration of 6%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 2 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF and KF in a melting furnace,and then adding the aforementioned amount of Al₂O₃ to obtain a melt bymelting; and(2) raising the temperature of the melt prepared in step (1) to above760° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 760° C.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.39V, the powerconsumption for per ton of aluminum is 10979 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.82%.

Embodiment 3

Fe, Cu, Ni and Sn metal blocks are mixed based on 25 wt % of Fe, 46.8 wt% of Cu, 28 wt % of Ni and 0.2 wt % of Sn, the mixture is molten byheating at high temperature and then subjected to casting to obtain ananode 3. The anode has a density of 8.2/cm³, a specific resistivity of72 μΩ·cm and a melting point of 1350° C.

The components of the electrolyte in this embodiment are as follows: 32%of NaF, 57% of AlF₃, 3% of LiF, 4% of KF and 4% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.12.

The performances of the electrolyte in this embodiment are measured andthe measurement result is that the liquidus temperature of theelectrolyte in this embodiment is 640° C. The electrolyte has anelectric conductivity of about 1.6 Ω⁻¹·cm⁻¹, a density of about 2.03g/cm³ and an alumina saturation concentration of 5%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 3 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF, KF and Al₂O₃ in a meltingfurnace so as to form a melt; and(2) raising the temperature of the melt prepared in step (1) to above730° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 730° C., wherein Al₂O₃ is quantitativelysupplied in the electrolysis process.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.15V, the powerconsumption for per ton of aluminum is 10202 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.85%.

Embodiment 4

Fe, Cu, Ni and Sn metal blocks are mixed based on 24.2 wt % of Fe, 60 wt% of Cu, 14 wt % of Ni and 0.2 wt % of Sn, the mixture is molten byheating at high temperature, 1.8 wt % of Al metal block is then addedfor continuous melting and mixing, and finally, 0.8 wt % of Y metalblock is added for melting and mixing and an anode 4 is obtained bycasting of the mixture. The anode has a density of 8.3/cm³, a specificresistivity of 68 μΩ·cm and a melting point of 1360° C.

The components of the electrolyte in this embodiment are as follows: 32%of NaF, 57% of AlF₃, 3% of LiF, 4% of KF and 4% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.12.

The performances of the electrolyte in this embodiment are measured andthe measurement result is that the liquidus temperature of theelectrolyte in this embodiment is 640° C. The electrolyte has anelectric conductivity of about 1.8 Ω⁻¹·cm⁻¹, a density of about 2.04g/cm³ and an alumina saturation concentration of 6%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 4 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF, KF and Al₂O₃ in a meltingfurnace so as to form a melt; and(2) raising the temperature of the melt prepared in step (1) to above750° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 750° C., wherein Al₂O₃ is quantitativelysupplied in the electrolysis process.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.12V, the powerconsumption for per ton of aluminum is 10105 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.8%.

Embodiment 5

Fe, Cu, Ni and Sn metal blocks are mixed based on 40 wt % of Fe, 36 wt %of Cu, 14.9 wt % of Ni and 5 wt % of Sn, the mixture is molten byheating at high temperature, 0.1 wt % of Al metal block is then addedfor continuous melting and mixing, and finally, 0.1 wt % of Y metalblock is added for melting and mixing and an anode 5 is obtained bycasting of the mixture. The anode has a density of 8.1/cm³, a specificresistivity of 76.8 μΩ·cm and a melting point of 1386° C.

The components of the electrolyte in this embodiment are as follows: 30%of NaF, 60% of AlF₃, 1% of LiF, 6% of KF and 3% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.0.

The performances of the electrolyte in this embodiment are measured andthe measurement result is that the liquidus temperature of theelectrolyte in this embodiment is 620° C. The electrolyte has anelectric conductivity of about 1.6 Ω⁻¹·cm⁻¹, a density of about 2.03g/cm³ and an alumina saturation concentration of 5%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 5 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF, KF and Al₂O₃ in a meltingfurnace so as to form a melt; and(2) raising the temperature of the melt prepared in step (1) to above720° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 720° C., wherein Al₂O₃ is quantitativelysupplied in the electrolysis process.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.27V, the powerconsumption for per ton of aluminum is 10591 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.81%.

Embodiment 6

Fe, Cu, Ni and Sn metal blocks are mixed based on 25 wt % of Fe, 38 wt %of Cu, 28 wt % of Ni and 4 wt % of Sn, the mixture is molten by heatingat high temperature, 4 wt % of Al metal block is then added forcontinuous melting and mixing, and finally, 1 wt % of Y metal block isadded for melting and mixing and an anode 6 is obtained by casting ofthe mixture. The anode has a density of 8.2/cm³, a specific resistivityof 70 μΩ·cm and a melting point of 1365° C.

The components of the electrolyte in this embodiment are as follows: 38%of NaF, 54% of AlF₃, 4% of LiF, 1% of KF and 3% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.4.

The performances of the electrolyte in this embodiment are measured andthe measurement result is that: the liquidus temperature of theelectrolyte in this embodiment is 670° C. The electrolyte has anelectric conductivity of about 1.8 Ω⁻¹·cm⁻¹, a density of about 2.05g/cm³ and an alumina saturation concentration of 6%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 6 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF, KF and Al₂O₃ in a meltingfurnace so as to form a melt; and(2) raising the temperature of the melt prepared in step (1) to above760° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 760° C., wherein Al₂O₃ is quantitativelysupplied in the electrolysis process.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.35V, the powerconsumption for per ton of aluminum is 10850 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.83%.

Embodiment 7

Fe, Cu, Ni and Sn metal blocks are mixed based on 40 wt % of Fe, 36.5 wt% of Cu, 18 wt % of Ni and 3 wt % of Sn, the mixture is molten byheating at high temperature, 1.5 wt % of Al metal block is then addedfor continuous melting and mixing, and finally, 1 wt % of Y metal blockis added for melting and mixing and an anode 7 is obtained by casting ofthe mixture. The anode has a density of 8.1/cm³, a specific resistivityof 76.8 μΩ·cm and a melting point of 1386° C.

The components of the electrolyte in this embodiment are as follows: 34%of NaF, 49% of AlF₃, 5% of LiF, 6% of KF and 6% of Al₂O₃, wherein themolar ratio of NaF to aluminum fluoride AlF₃ is 1.39.

The performances of the electrolyte in this embodiment are measured andthe measurement result is that the liquidus temperature of theelectrolyte in this embodiment is 660° C. The electrolyte has anelectric conductivity of about 1.8 Ω⁻¹·cm⁻¹, a density of about 2.05g/cm³ and an alumina saturation concentration of 6%.

The process using the electrolyte in the present invention for aluminumelectrolysis is as follows:

(1) by means of the anode 7 and the carbon body cathode, melting theaforementioned amounts of NaF, AlF₃, LiF, KF and Al₂O₃ in a meltingfurnace so as to form a melt; and(2) raising the temperature of the melt prepared in step (1) to above760° C. in the melting furnace, then pouring the melt into theelectrolytic cell, switching on the power supplies of the anode and thecathode, and carrying out electrolysis for 40 hours while thetemperature is maintained at 760° C., wherein Al₂O₃ is quantitativelysupplied in the electrolysis process.

There is no crust at the bottom of the cell body in the electrolysisprocess, the cell voltage of the electrolytic cell is 3.38V, the powerconsumption for per ton of aluminum is 10947 kw·h in the electrolysisprocess, and the prepared aluminum has a purity of 99.8%.

The electrolytic cell in the aforementioned embodiments is any of theelectrolytic cells in the present invention.

Detailed description has been made to the specific contents of thepresent invention in the aforementioned embodiments, and it should beunderstood by those skilled in this art that modifications and detailvariations in any form based upon the present invention pertain to thecontents that the present invention seeks to protect.

1. An electrolytic cell for aluminum electrolysis, comprising: a cell body, an anode and a cathode being arranged inside the cell body, the cell body being further filled with an electrolyte; the anode being arranged above the cell body, and at least a part of the anode being immersed in the electrolyte; the cathode being arranged at the bottom of the electrolytic cell and covered by a certain amount of aluminum liquid; the electrolyte being located between the anode and the cathode; wherein the anode contains the components including Fe, Cu, Ni and Sn, wherein Fe and Cu serve as primary components; and the electrolyte is composed of 30-38 wt % of NaF, 49-60 wt % of AlF₃, 1-5 wt % of LiF, 1-6 wt % of KF and 3-6 wt % of Al₂O₃, wherein the molar ratio of NaF to AlF₃ is 1.0-1.52.
 2. The electrolytic cell according to claim 1, wherein the bottom surface of the anode is kept parallel to the cell body, and an insulating layer is arranged on the inner sidewall of the cell body and is used for isolating oxygen or the electrolyte from a carbon block.
 3. The electrolytic cell according to claim 1, wherein a cell cover is arranged at the upper end of the cell body and is provided with a vent and a feeding hole; a cathode bar is arranged inside the cathode, one end of the anode penetrates through the cell cover and is connected and provided with a binding post for connection with a power supply.
 4. The electrolytic cell according to claim 1, wherein the mass ratio of Fe to Cu to Sn is (23-40):36-60):(0.2-5).
 5. The electrolytic cell according to claim 1, wherein the components of the anode further include Ni.
 6. The electrolytic cell according to claim 5, wherein the anode is composed of Fe, Cu, Ni and Sn, wherein the content of Fe is 23-40 wt %, the content of Cu is 36-60 wt %, the content of Ni is 14-28 wt % and the content of Sn is 0.2-5 wt %.
 7. The electrolytic cell according to claim 5, wherein the components of the anode further include Al and Y.
 8. The electrolytic cell according to claim 7, wherein the anode is composed of Fe, Cu, Ni, Sn, Al and Y, wherein the content of Fe is 23-40 wt %, the content of Cu is 36-60 wt %, the content of Ni is 14-28 wt %, the content of Al is more than zero and less than or equal to 4 wt %, the content of Y is more than zero and less than or equal to 2 wt %, and the content of Sn is 0.2-5 wt %.
 9. The electrolytic cell according to claim 1, wherein the molar ratio of NaF to AlF₃ is 1.12-1.52.
 10. The electrolytic cell according to claim 1, wherein the liquidus temperature of the electrolyte is 620-670° C.
 11. An electrolysis process using the electrolytic cell according to claim 1, comprising the steps of: (1) adding specified amounts of NaF, AlF₃, LiF, KF and Al₂O₃ to a melting furnace for mixing and melting to form a melt; or adding specified amounts of NaF, AlF₃, LiF and KF to a melting furnace for mixing and melting, and then adding Al₂O₃ to obtain a melt; and (2) raising the temperature of the melt prepared in step (1) to above 720-760° C., and then, pouring the melt into the electrolytic cell and carrying out electrolysis while the temperature is maintained at 720-760° C.
 12. The electrolysis process according to claim 11, wherein the electrolysis temperature is 730-750° C.
 13. The electrolysis process according to claim 11, wherein Al₂O₃ is quantitatively supplied in the electrolysis process.
 14. The electrolytic cell according to claim 2, wherein a cell cover is arranged at the upper end of the cell body and is provided with a vent and a feeding hole; a cathode bar is arranged inside the cathode, one end of the anode penetrates through the cell cover and is connected and provided with a binding post for connection with a power supply.
 15. The electrolytic cell according to claim 2, wherein the mass ratio of Fe to Cu to Sn is (23-40):(36-60):(0.2-5).
 16. The electrolytic cell according to claim 3, wherein the mass ratio of Fe to Cu to Sn is (23-40):(36-60):(0.2-5).
 17. The electrolytic cell according to claim 2, wherein the components of the anode further include Ni.
 18. The electrolytic cell according to claim 3, wherein the components of the anode further include Ni.
 19. The electrolytic cell according to claim 4, wherein the components of the anode further include Ni.
 20. The electrolytic cell according to claim 1, wherein the components of the anode further include Al and Y. 